diff options
Diffstat (limited to 'vendor/github.com/btcsuite/btcd/btcec/ciphering.go')
-rw-r--r-- | vendor/github.com/btcsuite/btcd/btcec/ciphering.go | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/vendor/github.com/btcsuite/btcd/btcec/ciphering.go b/vendor/github.com/btcsuite/btcd/btcec/ciphering.go new file mode 100644 index 000000000..b18c9b7a3 --- /dev/null +++ b/vendor/github.com/btcsuite/btcd/btcec/ciphering.go @@ -0,0 +1,216 @@ +// Copyright (c) 2015-2016 The btcsuite developers +// Use of this source code is governed by an ISC +// license that can be found in the LICENSE file. + +package btcec + +import ( + "bytes" + "crypto/aes" + "crypto/cipher" + "crypto/hmac" + "crypto/rand" + "crypto/sha256" + "crypto/sha512" + "errors" + "io" +) + +var ( + // ErrInvalidMAC occurs when Message Authentication Check (MAC) fails + // during decryption. This happens because of either invalid private key or + // corrupt ciphertext. + ErrInvalidMAC = errors.New("invalid mac hash") + + // errInputTooShort occurs when the input ciphertext to the Decrypt + // function is less than 134 bytes long. + errInputTooShort = errors.New("ciphertext too short") + + // errUnsupportedCurve occurs when the first two bytes of the encrypted + // text aren't 0x02CA (= 712 = secp256k1, from OpenSSL). + errUnsupportedCurve = errors.New("unsupported curve") + + errInvalidXLength = errors.New("invalid X length, must be 32") + errInvalidYLength = errors.New("invalid Y length, must be 32") + errInvalidPadding = errors.New("invalid PKCS#7 padding") + + // 0x02CA = 714 + ciphCurveBytes = [2]byte{0x02, 0xCA} + // 0x20 = 32 + ciphCoordLength = [2]byte{0x00, 0x20} +) + +// GenerateSharedSecret generates a shared secret based on a private key and a +// public key using Diffie-Hellman key exchange (ECDH) (RFC 4753). +// RFC5903 Section 9 states we should only return x. +func GenerateSharedSecret(privkey *PrivateKey, pubkey *PublicKey) []byte { + x, _ := pubkey.Curve.ScalarMult(pubkey.X, pubkey.Y, privkey.D.Bytes()) + return x.Bytes() +} + +// Encrypt encrypts data for the target public key using AES-256-CBC. It also +// generates a private key (the pubkey of which is also in the output). The only +// supported curve is secp256k1. The `structure' that it encodes everything into +// is: +// +// struct { +// // Initialization Vector used for AES-256-CBC +// IV [16]byte +// // Public Key: curve(2) + len_of_pubkeyX(2) + pubkeyX + +// // len_of_pubkeyY(2) + pubkeyY (curve = 714) +// PublicKey [70]byte +// // Cipher text +// Data []byte +// // HMAC-SHA-256 Message Authentication Code +// HMAC [32]byte +// } +// +// The primary aim is to ensure byte compatibility with Pyelliptic. Also, refer +// to section 5.8.1 of ANSI X9.63 for rationale on this format. +func Encrypt(pubkey *PublicKey, in []byte) ([]byte, error) { + ephemeral, err := NewPrivateKey(S256()) + if err != nil { + return nil, err + } + ecdhKey := GenerateSharedSecret(ephemeral, pubkey) + derivedKey := sha512.Sum512(ecdhKey) + keyE := derivedKey[:32] + keyM := derivedKey[32:] + + paddedIn := addPKCSPadding(in) + // IV + Curve params/X/Y + padded plaintext/ciphertext + HMAC-256 + out := make([]byte, aes.BlockSize+70+len(paddedIn)+sha256.Size) + iv := out[:aes.BlockSize] + if _, err = io.ReadFull(rand.Reader, iv); err != nil { + return nil, err + } + // start writing public key + pb := ephemeral.PubKey().SerializeUncompressed() + offset := aes.BlockSize + + // curve and X length + copy(out[offset:offset+4], append(ciphCurveBytes[:], ciphCoordLength[:]...)) + offset += 4 + // X + copy(out[offset:offset+32], pb[1:33]) + offset += 32 + // Y length + copy(out[offset:offset+2], ciphCoordLength[:]) + offset += 2 + // Y + copy(out[offset:offset+32], pb[33:]) + offset += 32 + + // start encryption + block, err := aes.NewCipher(keyE) + if err != nil { + return nil, err + } + mode := cipher.NewCBCEncrypter(block, iv) + mode.CryptBlocks(out[offset:len(out)-sha256.Size], paddedIn) + + // start HMAC-SHA-256 + hm := hmac.New(sha256.New, keyM) + hm.Write(out[:len(out)-sha256.Size]) // everything is hashed + copy(out[len(out)-sha256.Size:], hm.Sum(nil)) // write checksum + + return out, nil +} + +// Decrypt decrypts data that was encrypted using the Encrypt function. +func Decrypt(priv *PrivateKey, in []byte) ([]byte, error) { + // IV + Curve params/X/Y + 1 block + HMAC-256 + if len(in) < aes.BlockSize+70+aes.BlockSize+sha256.Size { + return nil, errInputTooShort + } + + // read iv + iv := in[:aes.BlockSize] + offset := aes.BlockSize + + // start reading pubkey + if !bytes.Equal(in[offset:offset+2], ciphCurveBytes[:]) { + return nil, errUnsupportedCurve + } + offset += 2 + + if !bytes.Equal(in[offset:offset+2], ciphCoordLength[:]) { + return nil, errInvalidXLength + } + offset += 2 + + xBytes := in[offset : offset+32] + offset += 32 + + if !bytes.Equal(in[offset:offset+2], ciphCoordLength[:]) { + return nil, errInvalidYLength + } + offset += 2 + + yBytes := in[offset : offset+32] + offset += 32 + + pb := make([]byte, 65) + pb[0] = byte(0x04) // uncompressed + copy(pb[1:33], xBytes) + copy(pb[33:], yBytes) + // check if (X, Y) lies on the curve and create a Pubkey if it does + pubkey, err := ParsePubKey(pb, S256()) + if err != nil { + return nil, err + } + + // check for cipher text length + if (len(in)-aes.BlockSize-offset-sha256.Size)%aes.BlockSize != 0 { + return nil, errInvalidPadding // not padded to 16 bytes + } + + // read hmac + messageMAC := in[len(in)-sha256.Size:] + + // generate shared secret + ecdhKey := GenerateSharedSecret(priv, pubkey) + derivedKey := sha512.Sum512(ecdhKey) + keyE := derivedKey[:32] + keyM := derivedKey[32:] + + // verify mac + hm := hmac.New(sha256.New, keyM) + hm.Write(in[:len(in)-sha256.Size]) // everything is hashed + expectedMAC := hm.Sum(nil) + if !hmac.Equal(messageMAC, expectedMAC) { + return nil, ErrInvalidMAC + } + + // start decryption + block, err := aes.NewCipher(keyE) + if err != nil { + return nil, err + } + mode := cipher.NewCBCDecrypter(block, iv) + // same length as ciphertext + plaintext := make([]byte, len(in)-offset-sha256.Size) + mode.CryptBlocks(plaintext, in[offset:len(in)-sha256.Size]) + + return removePKCSPadding(plaintext) +} + +// Implement PKCS#7 padding with block size of 16 (AES block size). + +// addPKCSPadding adds padding to a block of data +func addPKCSPadding(src []byte) []byte { + padding := aes.BlockSize - len(src)%aes.BlockSize + padtext := bytes.Repeat([]byte{byte(padding)}, padding) + return append(src, padtext...) +} + +// removePKCSPadding removes padding from data that was added with addPKCSPadding +func removePKCSPadding(src []byte) ([]byte, error) { + length := len(src) + padLength := int(src[length-1]) + if padLength > aes.BlockSize || length < aes.BlockSize { + return nil, errInvalidPadding + } + + return src[:length-padLength], nil +} |